1. Field
The present disclosure generally relates to systems and methods of pumping fluid and, in particular, relates to the delivery of medical fluid by an infusion pump.
2. Background
Infusion pumps have become commonplace within the healthcare world as a way to precisely administer intravenous (IV) fluids. Use of a pump in place of an elevated fluid container with a simple roller clamp to control the flow of the IV fluid allows more accurate and consistent control of the rate of delivery of the fluid to the patient.
The assembly of tubing, valves, fittings, and needles that connect the fluid container to the patient may be referred to as an “IV set.” IV sets are typically disposable to reduce the risk of infection and contamination. When used with an infusion pump, the IV set includes a segment intended to be manipulated by the pump to cause the fluid to flow at a controlled rate. A typical IV pump system is shown in FIG. 1 that depicts a patient 10 receiving a medical fluid from a fluid container 14 through an IV set 18. A pumping segment (not shown) of IV set 18 is located inside pumping module 20 of IV pump 12. The pumping module is controlled by pump controller 16.
For a peristaltic type of IV pump, the pumping segment may be as simple as a length of tubing that is fitted into the pumping compartment. FIG. 2 depicts an example IV set 18 having a bag spike 2 configured to connect to an IV bag (not shown) and pierce the seal of the bag, a length of tubing 4, a pumping segment 8, another length of tubing 4, and, in this example, a needleless connector 6. Pumping segment 8 includes locating fittings 5A and 5B at the ends of pumping segment 8, wherein the locating fittings 5A-5B match features on pumping module 20 of FIG. 1 to properly locate and retain the pumping segment 18 in the pumping module 20. IV set 18 also includes a clamp 9 that, when closed, blocks flow through tube 4.
Many IV pumps use pumping techniques, such as the peristaltic manipulation of a flexible tube, that deliver intermittent flow rather than continuous flow. While this may average out to be the desired rate of delivery, the instantaneous delivery rate varies from zero to as much as twice the nominal rate. This becomes even more apparent at very low delivery rates, as the pumping technique may delivery a periodic bolus of medical fluid rather than the desired continuous delivery at the nominal rate. For some patients, such as neonatal patients, this level of variation may be unacceptable. It is desirable to be able to provide a more continuous delivery at a more constant flow rate.
Another challenge common to existing IV pumps is that the manipulation of the pumping segment repeatedly compresses a flexible element of the pumping segment and relies on the flexible material to recover its original shape between compression strokes. The amount of recovery of the original shape affects the internal volume of the flexible element and therefore the amount of fluid pumped per compression stroke.